When I was a bookseller we had a game to idle away the odd quiet moment at the till on a Saturday. Bookshops shelve books alphabetically by author, a logical thing to do given the belief that customers will at least know who wrote the book they're after. As anyone who's ever been a bookseller will know, this applies to only about half of all customers. The rest of the time is spent trying to guess which title is being referred to by "It's by that Scottish writer, the one with the nose," or "It was mentioned on Front Row. Or was it Start the Week?" or the truly surpassing "It's big and yellow. And square."

So those idle moments were spent trying to work out the most ridiculous and useless classification system. The winning plan was to have books shelved according to the number of copies in stock; a system that not only was utterly useless for anything but stocktake, but also meant moving all the other copies of a title from "24 copies" to "23 copies" if one were to be sold. And then back again when it was returned as an unwanted gift.

My favourite system, however, was length of book; not only would the visual impact on the shelf be rather striking, I also fancied that the books down the short end would contain some of the best writing to be had. There would be The Old Man and the Sea, Utz, and Heart of Darkness, and there too would be Song for Eloise, a quiet triumph that shows once again that just because a book is short does not mean it cannot deal with the profound, cannot touch and move us, cannot resonate.

Taking Tristan and Isolde as her inspiration, Leigh Sauerwein creates a series of intertwining tableaux through which at least five lifetimes are shown to us. Set in 12th-century France, against the backdrop of the crusades, Song for Eloise is an elegant and haunting story through which drifts a question that will always possess us: what is it like to be unable to be with the one you love? Eloise is 15 when she is married off for political union to Robert of Rochefort, a man twice her age. Robert is a brutish, sombre soldier whose loyalty to Lord Baudoin, Eloise's father, is rewarded not only with a castle, but a wife to boot.

So Eloise leaves home for the windswept castle in the hills, and as the years pass she does her duty as a wife. She conceives and bears Robert a son, and yet neither of them is happy. Robert agonises over the emptiness in his young bride's eyes, a dullness where once the light sparkled. After a chance meeting in the forest, he hires a young troubadour and his juggling companion to come to the castle, in a desperate attempt to give Eloise some joy. Robert however is unaware that Thomas, the troubadour, and Eloise were once childhood sweethearts. What plays out is inevitable, yet no less gripping for that - perhaps more so - and as the fates of Eloise, Thomas, and Robert descend upon them we are unable to look away.

The book is written as a series of small snapshots, surely intentionally reminiscent of the kind of tapestries that would be hanging in every room in Robert's castle, a poetic device that enables Sauerwein to cover much ground with a deceptively light hand. Perhaps here is the only weakness of the short book; it's over all too soon.

The short book needs to be savoured. Bookshops are fuller than ever these days of fat tomes that waste words as if they were easy to come by, only encouraging the reader to glide as quickly as possible through their verbiage. Song for Eloise, meanwhile, takes its rightful place in my fantasy shop. It's just over there, under the sign Short Books: Read Slowly.